In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and LTE-Advanced (LTE-A) systems, a Transmission Time Interval (TTI) is a basic unit of downlink and uplink transmission scheduling in the time domain. For example, in LTE/LTE-A Frequency Division Duplex (FDD) systems, the downlink and uplink transmission scheduling is divided into radio frames with a length of 10 ms in a time dimension. Each radio frame includes 10 subframes, and a length of the TTI is equal to a length of each subframe, which is equal to 1 ms. Each subframe includes two time slots, each of which has a length of 0.5 ms. Each downlink time slot contains 7 Orthogonal Frequency Division Multiplexing (OFDM) symbols (6 OFDM symbols under extended cyclic prefixes); and each uplink time slot contains 7 Single Carrier-Frequency Division Multiplexing Access (SC-FDMA) symbols (6 SC-FDMA symbols under extended cyclic prefixes).
The subsequent evolution of 3GPP, for example, the 5th generation (5G) mobile communication system, will support higher rate (Gbps), massive link (1 M/Km2), ultralow latency (1 ms), higher reliability, hundredfold increase in energy efficiency, and the like than the LTE/LTE-A systems to support new changes in demands. The ultralow latency is a key indicator of the 5G technology, which directly affects the development of latency-limited services such as car networking, industrial automation, remote control, and smart power grids.
However, an existing TTI with a length of 1 ms will not meet the demand. An effective solution is to reduce the length of the TTI. For example, if the length of the TTI is reduced from the existing length of 1 ms to 0.5 ms or even to one or two OFDM symbols, the minimum scheduling time can be reduced significantly, and further the single transmission latency is reduced by significantly. When the length of the TTI is greater than or equal to the lengths of the three symbols, it is difficult to achieve a unidirectional air interface ultralow latency indicator of 1 ms. Further, in order to achieve higher transmission efficiency, reducing the length of the TTI to the lengths of 2 OFDM/SC-FDMA symbols is one reasonable solution.
In the related art, when the length of the TTI is two symbols, a transmission structure used to transmit an Acknowledgement (ACK) message and a Negative Acknowledgement (NACK) message in a Physical Uplink Control Channel (PUCCH) will not be directly usable. Meanwhile, the reduction in the number of the symbols within the TTI will cause excessive overhead of reference symbols (RS).
For a problem that when the length of the transmission time interval is two symbols, the transmission structure for transmitting the ACK message and the NACK message is imperfect in the prior art, there is no effective solution at present.